title: Novel chimeric beta-lactamase CTX-M-64, a hybrid of CTX-M-15-like and CTX-M-14 beta-lactamases, found in a Shigella sonnei strain resistant to various oxyimino-cephalosporins, including ceftazidime.
abstract: The plasmid-mediated novel beta-lactamase CTX-M-64 was first identified in Shigella sonnei strain UIH-1, which exhibited resistance to cefotaxime (MIC, 1,024 microg/ml) and ceftazidime (MIC, 32 microg/ml). The amino acid sequence of CTX-M-64 showed a chimeric structure of a CTX-M-15-like beta-lactamase (N- and C-terminal moieties) and a CTX-M-14-like beta-lactamase (central portion, amino acids 63 to 226), suggesting that it originated by homologous recombination between the corresponding genes. The introduction of a recombinant plasmid carrying bla(CTX-M-64) conferred resistance to cefotaxime in Escherichia coli, and the activities of cefotaxime and ceftazidime were restored in the presence of clavulanic acid. Of note, CTX-M-64 production could also confer consistent resistance to ceftazidime, which differs from the majority of CTX-M-type enzymes, which poorly hydrolyze ceftazidime. These results were consistent with the kinetic parameters determined with the purified CTX-M-64 enzyme. The bla(CTX-M-64) gene was flanked upstream by an ISEcp1 sequence and downstream by an orf477 sequence. The sequence of the 45-bp spacer region between the right inverted repeat (IRR) of ISEcp1 and bla(CTX-M-64) was exactly identical to that of ISEcp1-bla(CTX-M-15-like). Moreover, the presence of a putative IRR of ISEcp1 at the right end of truncated orf477 is indicative of an ISEcp1-mediated transposition event in the bla(CTX-M-64) gene. The emergence of CTX-M-64 by probable homologous recombination would suggest the natural potential of an alternative mechanism for the diversification of CTX-M-type beta-lactamases.
authors.affiliation: Department of Bacterial Pathogenesis and Infection Control, National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Nagano
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nagano
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Wachino
authors.forename: Keiko
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Arakawa
mesh_terms: D000595:Amino Acid Sequence; D015139:Blotting, Southern; D002442:Ceftazidime / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012764:Shigella sonnei / Q000187:drug effects / Q000201:enzymology*; D001618:beta-Lactamases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D002511:Cephalosporins; D002442:Ceftazidime; C456080:beta-lactamase CTX-M-14; C473109:beta-lactamase CTX-M-15; D001618:beta-Lactamases